The fuselage structures of aircraft are usually lined with mat-like insulation packages that consist of a puffy mineral fiber material and welded cover films. These insulation packages fulfill several functions that, in addition to the thermal insulation of systems in the interior of the aircraft and of a passenger cabin formed in the fuselage structure, also include a sufficient protection against burn-through, a barrier function for condensate in order to protect systems and the cabin from dripping water and an acoustic insulation of the cabin. The fiber material used in conventional insulation packages restricts the air convection in the insulating mat and ensures a high thermal insulating effect due to this restricted air convection and its high heat transfer resistance. In an upper region of a fuselage structure of an aircraft, the outwardly directed film is usually realized in a waterproof fashion and therefore fulfills the function of a condensate barrier that protects the systems and the cabin from dripping water. The inwardly directed cover film of the insulation packages is usually realized in the form of a membrane or perforated and therefore permeable to air in order to ensure a pressure compensation between air enclosed in the insulation packages and the surroundings and to simultaneously prevent the insulation packages from inflating and shrinking during pressure variations in the fuselage structure.
The insulation packages are usually installed in an overlapping fashion in order to divert condensation water and to prevent this condensation water from being admitted into the cabin. The overlaps of the insulation packages are usually permeable to air and ensure a pressure compensation between air in the cabin and air enclosed between the insulation packages and the fuselage structure. During a pressure variation in the fuselage, this air permeability prevents undesirable compressive forces from acting upon the insulation packages and their fasteners.
Air enclosed between the insulation packages and a fuselage structure that is relatively cold during a flight is cooled off and, due to the increasing density, reaches lower-lying regions of the fuselage structure in the form of a convection current, wherein this air is then drawn into a recirculation circuit of an air-conditioning system of the aircraft and admixed to the supply air for the cabin. The convection current creates a suction effect that continuously draws warm and humid cabin air, among other things, through the overlaps of the insulation packages. The moisture contained in the cabin air condenses and freezes on the fuselage structure, and the air flowing along the fuselage structure is cooled off and partially dehumidified by the condensation process. This phenomenon leads to a circulatory convection current between the insulation packages and the fuselage structure.
Condensation water that precipitates on and drips off the fuselage structure is diverted into lower-lying regions of the fuselage structure by the condensate barrier, i.e., the outwardly directed waterproof film of the insulation packages.
The thermal insulation of the cabin relative to the cold fuselage wall is essentially achieved with the air cushion between the insulation packages and the fuselage structure, as well as the high heat transfer resistance of the insulation packages. Assuming the insulation packages have conventional dimensions, the location with the dew point temperature of the cabin air is situated within the insulation packages when the fuselage structure is very cold. Due to pressure variations and diffusion effects, warm and humid cabin air is continuously admitted into the insulation packages through the perforated film facing the cabin. Condensation takes place if this air penetrates into the insulation material up to the location with the dew point temperature. Due to their strong capillary action, the mineral fibers absorb drops of the condensate and prevent the drainage thereof. The steadily increasing water content in the insulation packages resulting thereof reduces the insulating effect and shifts the location of the dew point toward the cabin such that the condensation and the resulting water absorption of the insulation packages are additionally increased. If the drying time does not suffice, the insulation packages therefore can absorb significant quantities of water such that their weight may dramatically increase and the efficiency of the insulation packages may steadily decrease.
EP 1 124 720 B1 and US 20040175516 A1 disclose an insulation arrangement for the interior insulation of an aircraft, in which insulation packages are completely enclosed by a film cover and arranged within an intermediate space, wherein the film cover is realized with a film material that allows the diffusion of gases and liquids.
In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.